Visual and semiquantitative analysis of F-18-fluorodeoxyglucose positron emission tomography using a partial-ring tomograph without attenuation correction to differentiate benign and malignant pulmonary nodules

Objective: Many studies have reported the use of attenuation-corrected posi tron emission tomography with F-18-fluorodeoxyglucose (FDG PET) with full-r ing tomographs to differentiate between benign and malignant pulmonary nodu les. We sought to evaluate FDG PET using a partial-ring tomograph without a ttenuation correction. Methods: A retrospective review of PET images from 7 7 patients (range 38-84 years of age) with proven benign or malignant pulmo nary nodules was undertaken. All images were obtained using a Siemens/CTI E CAT ART tomograph, without attenuation correction, after 185 MBq F-18-FDG w as injected. Images were visually graded on a 5-point scale from "definitel y malignant" to "definitely benign," and lesion-to-background (LB) ratios w ere calculated using region of interest analysis. Visual and semiquantitati ve analyses were compared using receiver operating characteristic analysis. Results: Twenty lesions were benign and 57 were malignant. The mean LB rat io for benign lesions was 1.5 (range 1.0-5.7) and for malignant lesions 5.7 (range 1.2-14.1) (p<0.001). The area under the ROC curve for LB ratio anal ysis was 0.95, and for visual analysis 0.91 (p=0.39). The optimal cut-off r atio with LB ratio analysis was 1.8, giving a sensitivity of 95% and a spec ificity of 85%. For lesions thought to be "definitely malignant" on visual analysis, the sensitivity was 93% and the specificity 85%. Three proven inf ective lesions were rated as malignant by both techniques (LB ratio 2.6-5.7 ). Conclusions: FDG PET without attenuation correction is accurate for diff erentiating between benign and malignant lung nodules. Results using simple LB ratios without attenuation correction compare favourably with the publi shed sensitivity and specificity for standard uptake ratios. Visual analysi s is equally accurate.